1. Technical Field
This invention relates generally to componentry for radio controlled models, and more particularly to an RC servo.
2. Background Information
Radio controlled or RC servos drive various control linkages on radio controlled models, such as the steering linkage on a model car or the control surface linkages on a model airplane or model boat. With a handheld transmitter, the user transmits a signal to a receiver mounted on the model and the receiver produces a control signal to which the RC servo responds to drive the control linkage accordingly.
The housing of a typical RC servo for a radio controlled car, for example, may be about 4.times.4.times.2 cm and contain a battery-powered motor for this purpose. A gear train within the housing couples the motor to an output shaft that extends through the housing where it can be coupled to the steering linkage by suitable components, including an output arm mounted on the output shaft. When the motor moves, the output arm moves to drive the steering linkage.
Feedback control circuitry within the housing operates conventionally to sense the position of the output shaft and drive the motor until the output shaft is in a desired position. A position sensor in the form of a potentiometer coupled to the output shaft may be used to sense the output shaft position for this purpose. Known electrical circuitry produces an error signal indicative of the difference between output shaft position and the desired position, and the error signal is used to produce a motor control signal that drives the motor until the output shaft has moved to the desired position.
This results in accurate control of the output shaft according to well known principles of feedback control. However, there are certain problems to be overcome. For example, the model car may run into a rut in the road or other obstacle that results in a large transient force being transmitted through the steering linkage to the RC servo. Similar transient forces may result in other radio controlled models as well, and these forces may damage the RC servo.
To overcome this problem, some control linkages, such as the steering linkage of some existing radio controlled model cars, include a spring-coupled section for smoothing transient forces so that they do not damage the RC servo. It may take the form of a spring-coupled output arm, for example. When a transient force is transmitted along the steering linkage to the spring-coupled output arm, the spring resiliently deforms to provide a filtering effect so that the transient force is not rigidly coupled to the RC servo. In most cases, this helps prevent damage to the RC servo.
However, utilizing a spring-coupled section of linkage introduces other problems that need to be overcome. First, it introduces sloppiness or play in the linkage such that the linkage does not always return to a center or zero point. As a result, the spring-coupled section may result in inaccurate positioning of a steering linkage or of control surface linkages.
In addition, a spring-coupled section may mean more parts, expense, weight, and space. Each of these should be kept to a minimum.
Furthermore, it may be intended that the spring-coupled section of linkage be suitable for use with various RC servos, instead of designing, manufacturing, and selling a different spring-coupled section for each of various available RC servos. Thus, the spring-coupled section must be designed to protect the most fragile of available RC servos so that it may over-protect the less fragile RC servos.
Moreover, if the transient force is large enough, the spring-coupled section may be driven to its limit. In other words, the force may fully extend or compress the spring so that the force is still rigidly transmitted to the RC servo despite the spring-coupled section.
Consequently, it is desirable to have a new and improved RC servo that overcomes these concerns.